When two visitor profiles are merged, a merge strategy is followed. The merge strategy is determined by a special tag that is assigned by your application manager or developer to each profile property in a plugin. The merging strategy specifies, among other things, whether one property wins out over another, whether both values are kept, whether numerical values are summed together, and so forth. Determining what the merge strategy is for a profile property is discussed in full in the section Merge Strategy. Determining that two visitor profiles belong to the same visitor is the key to profile merging. For best results, you should target profile properties that are most guaranteed to be unique like, for example, the e-mail address of the visitor. While two profiles containing the same first and last name likely means that the visitor profiles belong to the same person, it is at the same time possible that you are dealing with two different visitors who have the same first and last name. It is therefore important that you create merge rules that are logical and that are most likely to uniquely identify visitor profiles that belong to the same person. When the profile merge rules are not able to determine that a visitor with multiple profiles is the same person, they will continue to have multiple visitor profiles that are updated based on the channel(s) they visit in your BlueConic universe.
When two visitor profiles are merged, both profiles are kept. The profile properties and their values that do not exist in the visitor profile that is merged into will be added. The values of the profile properties that are shared by both visitor profiles are merged one by one according to the merge strategy assigned to the property in the plugin. Normally, the newest profile becomes the active profile and the older profile becomes inactive. All profile properties in the older profile are set to null except for two. The only properties that have a value in the older visitor profile are the profile ID and a property called "replaced by" that contains a reference to the newer visitor profile. For example:
The following two profiles, Profile A and Profile B are determined to belong to the same person on the basis of matching e-mail addresses:
The profiles are merged together. The result after the merge is: